A once-in-a-thousand-years chance to study what might kill us
Once every thousand years, a mountain-sized rock draws close enough to Earth to be seen with the naked eye — and in 2029, that moment arrives. Asteroid Apophis, 350 meters wide, will pass within 31,000 kilometers of our planet, closer than many orbiting satellites, carrying with it a small but unresolved question about 2068: will it return, and will it strike? Scientists gathered in late 2020 not merely to marvel at the encounter, but to design the instruments, spacecraft, and strategies that might finally answer that question before the window closes.
- A 350-meter asteroid ranked third on NASA's hazard list will pass closer to Earth than GPS satellites in 2029 — a proximity that happens perhaps once a millennium.
- Despite being discovered sixteen years ago, Apophis remains poorly understood: its shape, composition, internal structure, and precise orbit are all still uncertain, and that uncertainty carries real consequences for 2068.
- Earth's gravity during the flyby will stress and reshape the asteroid in real time — triggering potential avalanches, altering its spin, and shifting the very orbital mechanics that determine whether it becomes a threat.
- Nearly 200 scientists convened to propose a coordinated response: radar telescopes, redirected spacecraft, robotic landers, seismometers, and laser reflectors — all aimed at transforming a rare flyby into a planetary defense intelligence mission.
- The next nine years are the preparation window — and whether humanity launches the right missions in time will determine how much we know, and how ready we are, when Apophis swings past.
In April 2029, asteroid 99942 Apophis — roughly 350 meters across — will pass within 31,000 kilometers of Earth, closer than many of the satellites we rely on daily. Visible to the naked eye from a clear sky, it will be the closest approach of an asteroid this size in perhaps a thousand years. But Apophis is not merely a spectacle. It sits third on NASA's list of potentially hazardous near-Earth objects, carrying odds between one in 150,000 and one in 530,000 of striking Earth in 2068. Such an impact would release energy equivalent to 1,150 megatons of TNT — roughly 3,800 times the force of Hiroshima.
Recognizing the 2029 flyby as a rare scientific and strategic opportunity, the Lunar and Planetary Institute convened a virtual workshop in late 2020, drawing nearly 200 specialists in asteroids, radar astronomy, robotics, and aerospace engineering. Their shared goal: to determine how humanity might best study Apophis during its close approach. Despite being discovered in 2004, the asteroid remains poorly known — its shape, composition, internal structure, and precise orbit are all uncertain. Scientists suspect it may resemble a cigar or two objects touching end-to-end, but are far from sure.
The 2029 encounter itself will be a dynamic event. Earth's gravity will stress Apophis, potentially triggering surface avalanches, shifting loose material, and altering its rotation — changes that could meaningfully affect whether the asteroid poses a danger four decades later. To capture these changes, researchers proposed layered observation strategies. Ground-based radar facilities in California, Australia, Massachusetts, and Germany could image the asteroid's surface at high resolution. But workshop participants argued that only spacecraft could truly close the knowledge gap.
Proposals ranged from a small rendezvous craft weighing under 180 kilograms to a solar-sail-powered vessel deploying a mobile lander. NASA's OSIRIS-REx, currently at asteroid Bennu, was suggested as a candidate for redirection toward Apophis. Other ideas included robotic hoppers, seismometer-equipped impactors to map the interior, and clusters of laser reflectors launched to the surface in 2028 to track orbital shifts for years afterward. The challenge ahead is coordination — turning these concepts into real missions, avoiding duplication, and ensuring observations span before, during, and after the flyby. The next nine years will reveal whether humanity is prepared to meet this moment with the tools and knowledge it demands.
In nine years, an asteroid the size of a small mountain will pass closer to Earth than many of the satellites we depend on every day. The object is 99942 Apophis, and on April 12, 2029, it will come within 31,000 kilometers of our planet—a tenth of the distance to the Moon. For an asteroid measuring roughly 350 meters across, this is an extraordinarily rare event, one that occurs perhaps once every thousand years. On that day, if the sky is clear, you will be able to see it without a telescope.
But Apophis is not merely a celestial curiosity. It ranks third on NASA's list of potentially hazardous near-Earth objects, and while the odds are small—somewhere between one in 150,000 and one in 530,000—there exists a genuine possibility that this asteroid could strike Earth in 2068. If it did, the impact would release energy equivalent to 1,150 megatons of TNT, roughly 3,800 times the force of the atomic bomb dropped on Hiroshima. The 2029 flyby, therefore, represents something far more significant than a rare astronomical event: it is an opportunity to study a potentially catastrophic threat in unprecedented detail, to measure its properties, to understand how Earth's gravity will alter its trajectory, and to refine the calculations that determine whether it poses a real danger.
Recognizing this moment, the Lunar and Planetary Institute convened a virtual workshop in late 2020 called "Apophis T-9 Years: Opportunities for Knowledge for Planetary Defense Science." Nearly 200 participants attended—asteroid specialists, astrophysicists, radar astronomers, roboticists, and engineers—to brainstorm how humanity might best use the 2029 encounter. Andrew Cheng, chief scientist at Johns Hopkins University's Applied Physics Laboratory, called it a "natural experiment," a chance to study both the exterior and interior of an object we know surprisingly little about. Apophis was discovered sixteen years earlier, yet our knowledge remains limited to vague measurements and grainy radar images. We do not know its precise orbit, its exact shape, its internal structure, its chemical composition, or how the irregular heat radiating from its surface—an effect called Yarkovsky—might be nudging it along a different path through space.
The scientists believe Apophis may be shaped like a cigar, possibly two objects touching end-to-end, similar in form to the comet Churyumov-Gerasimenko. But they are not certain. The list of unknowns is long and consequential. When Apophis swings past Earth, the planet's gravity will stress the asteroid in ways that could trigger small avalanches, shift surface material, alter its rotation, and change the very orbital mechanics that determine whether it will threaten us four decades hence. To understand these changes, researchers proposed a coordinated campaign of observation from the ground and from space.
From Earth, radar telescopes offer the most immediate tool. Marina Brozović, a radar scientist at NASA's Jet Propulsion Laboratory, explained that observations beginning in 2021—when Apophis would be about 16.9 million kilometers away—would provide the last detailed radar images before the close approach. By 2029, when the asteroid reaches its nearest point, ground-based facilities including Goldstone in California, the Canberra Deep Space Communication Complex, MIT's Haystack Observatory, and Germany's Tracking and Imaging Radar could scan Apophis's surface with extraordinary precision: more than 10,000 pixels at a resolution of 1,875 meters per pixel. This would reveal surface roughness, the distribution of regolith (loose surface material), and potentially the structure of the subsurface itself.
Yet ground-based observation, however sophisticated, has limits. Brent Barbee, an aerospace engineer from the University of Maryland, argued that only close-range spacecraft observations could truly reduce the uncertainties about Apophis's threat level. The workshop participants proposed an ambitious array of missions. One concept involved a small spacecraft weighing less than 180 kilograms that would rendezvous with Apophis six to eight months before its closest approach, collecting data continuously through the encounter. Another idea, proposed by Jan Thimo Grundmann of Germany's space agency, imagined a solar-sail-powered spacecraft hovering near the asteroid for an extended period, deploying a mobile lander to the surface. Dante Lauretta, a planetary scientist at the University of Arizona, suggested that NASA's OSIRIS-REx spacecraft—currently orbiting the asteroid Bennu—might be redirected to Apophis by 2029, carrying instruments that could map the asteroid's topology, chemistry, and mineralogy.
Other proposals ranged from the practical to the ingenious. Small robotic hoppers, similar to those used to explore the asteroid Ryugu, could be deployed across Apophis's surface. A sonde equipped with a seismometer could measure vibrations triggered by an active impactor, creating a map of the asteroid's interior. David Smith, a NASA researcher, proposed launching ten to twenty tiny laser reflectors onto Apophis's surface in 2028, allowing scientists to track the asteroid's movement for a decade or more and detect any shifts in surface integrity. Jay McMahon from the University of Colorado Boulder suggested soft robotics—flexible machines ideal for exploring small bodies, equipped with radar antennas, seismometers, and gravity-measurement tools.
The challenge now is to transform these concepts into actual missions, to coordinate efforts to avoid duplication, and to maximize the science gained from multiple spacecraft working in concert. Terik Daly, a planetary scientist at Johns Hopkins, emphasized the importance of observations before, during, and after the 2029 encounter, so that scientists can assess how the close approach has altered Apophis's orbital dynamics and threat potential. The next nine years will determine whether humanity is ready to meet this moment—whether we can build the tools, launch the missions, and gather the knowledge needed to understand whether Apophis truly threatens us, and if so, what we might do about it.
Citações Notáveis
A natural experiment and a rare opportunity to study the exterior and interior of the asteroid— Andrew Cheng, Johns Hopkins Applied Physics Laboratory
Only close-range spacecraft observations could truly reduce the uncertainties about Apophis's threat level— Brent Barbee, University of Maryland aerospace engineer
A Conversa do Hearth Outra perspectiva sobre a história
Why does this particular asteroid matter more than the thousands of others out there?
Because it's big enough to cause global catastrophe if it hits, and it's coming close enough that we can actually study it in detail. Most asteroids we never see clearly. This one will be visible to the naked eye.
But the odds of it hitting in 2068 are tiny—one in 150,000. Why spend billions on missions for something so unlikely?
Because if those odds are even slightly wrong, the consequences are unimaginable. And right now, we're working with incomplete information. The 2029 flyby is our chance to measure Apophis precisely enough to know whether those odds are really one in 150,000 or something worse. We can't make that decision without the data.
What happens to the asteroid when it passes so close to Earth?
Earth's gravity will pull on it, stress it, possibly trigger landslides on its surface. We don't know exactly how it will respond. That's partly why we need to watch it closely—to see how the encounter changes its orbit, its rotation, its physical integrity. Those changes matter for calculating whether it could hit us later.
These proposed missions sound expensive and risky. Why not just wait and see what happens in 2029?
Because passive observation from Earth, while useful, can only tell us so much. A spacecraft nearby could measure the asteroid's interior, its composition, how it deforms under stress. That knowledge is what lets us actually predict its future path and, if necessary, plan how to deflect it.
Deflect it? You mean push it out of the way?
Potentially, yes. But that's a conversation for later. First, we need to know what we're dealing with. That's what 2029 is really about—gathering the intelligence we need to make informed decisions if Apophis ever becomes a genuine threat.
What's the timeline looking like? Can all these missions actually happen?
That's the real question. Some proposals are more feasible than others. Ground-based radar observations can start next year. Spacecraft missions are harder—they take years to develop and launch. The window is tight, but not impossible. The next few years will show whether the scientific community can actually pull this off.